System for closely monitoring a blood pressure over an extended period of time



United States Patent (72] Inventor Jack L. Wilhelmson [56] References Cited Femon UNITED STATES PATENTS El 9. m- 2 3 1967 2710.001 6/1955 Freyburger 128/205 f 3 2,826,191 3/1958 Burns 128/205 Patented Dec.29, 1970 4 7 [73] Assi nee Bv mesne assi nments to 3l20846 2/196 Fletcher g ff L h I 3,126,886 3/1964 Karsh l28/2.05 "?1, e 3,137,292 6/1964 Richter 128/205 2,952,253 9/1960 Seligman etal 128/205 Jersey 3,104,661 9/1963 l-lalpern 128/2.05

Primary ExaminerWilliam E. Kamm Attorneys-Samuel L. Welt, Jon S. Saxe, Bernard S. Leon and 54 SYSTEM FOR CLOSELY MONITORING A BLOOD Frank PRESSURE OVER AN EXTENDED PERIOD OF g gfi 4Dmwin Fi ABSTRACT: A portable blood pressure monitor featuring g plural inflation sources set at different flow rates connected to [52] U.S.Cl 128/2.05 areservoir and cuff. The Korotkoff sound sensing channel and [51] Int. Cl A61b 5/02 the various valves are controlled by a timing circuit to permit [50] Field of Search 128/205 rapid as well as normal pressure buildup and release.

251/52 a/rce/M/lmme 1W0 s/a/mz off/Fame F/LTEKS 69 lie/v.52 28 36 33 J7 6/ a3 37/ flame/w: .98 sw/rm RELAY! x I :QQ: 9! A92 wan/s25 m/ E'ESE/ZVO/B CUFF MQLVE PATENTEUUEEZQEEB 3,550 582 SHEET 2 UF 2 FIG.2.

22 POWER present invention providesa sphygmomano tors-a bloodprjessure ofaperson at frequentintervals' over an '1" SYSTEM ron cLossLv MONITORING A aLoon nsssum: ovsn AN EXTENDED PERIOI) or TIME This invention relatesto improvements in Control Systems. More particularly, this invention relates to improvements in .control systems for sphygmomanome'ters. I I

, It is. therefore, an object of the present inviention to provide an improved control system'for'a sphygmomanometer.

lt isfrequently'desirable to monitor a blood pressureof -a person at frequent intervalsover an extended period of time. To obtainthis desirable result,'an inflatable cuff can be applied to anarm of that person'ga microphone can be disposed in engagement withthatfiarm distally of th' t inflatable cuff,

and thatinflatable cuff can "recurrently ocolude' an artery in that arm .to develop Korotkoff sounds wiich can be sensed'by that microphone. The pressure that is applie to the inflatable cuff also will be applied to a pressure-i dicating instrument;

. and that instrument will'indic'ate said ood'pressure' .of that person. Because the pressure that i used in a sphygmomanometer, to compress an artery s fficiently to develop Korotkofl' sounds,'is great enough to hal all venous flow in the arm of that person, itis important th t the sensing'of said blood pressurebe discontinued for finite pentiods of time. The

eter which moniextended period of time; but which protects that person by recurrently releasing all" of the pressure in the inflatable cuff thereof for finite'periods of time. As a result, that sphygmomanometer canmonitor a blood pressure of a person over an extended period of time withoutiany injury to that person.

' It is,:therefore, anobject of the present invention to provide a sphygmomanometer thatrn'onit'ors a blood'pressure of a person at frequent'intervals' over-an extended period of time, but

cuff thereof for finite periods of time.

which recurrently releases all of the pressure in the inflatable During the actual sensing of a blood pressure of a person, the inflatable cuff of the sphygm'omanometershould be inflat'ed at a relatively lowrate to prevent overshooting" of the pressure needed to cause Korotkoff sounds to develop; but a relatively low rate of inflation would needlessly prolongthe initial pressurization of the inflatable cuff after any period wherein all of the pressure was released from that inflatable operator of that sphygmomanometer to physically develop the pressure required by that inflatable cuff, and thus prevents automatic operation of that sphygmomanometer. The use of an air compressor keeps that sphygmomanometer from being readily portable. The sphygmomanometer provided by the present invention obviates all need of a resilient bulb or of an air'compressor to inflate the inflatable cuff thereof; and it does so by providing a small quantity of compressed gas to inflate that inflatable cuff. .That quantity. of compressed gas can be confined and held within a small space, and yet can provide recurrent pressurizations of the inflatable cuff of the sphygmomanometer for prolonged periods of time. It is. therefore,

an object of the present invention to provide a sphyg-- momanometer which usesa small quantity of compressed gas to'inflate the inflatable cuff thereof.

The compressed .gas used in the sphygmomanometer pro- 'vided bythe present invention is a readily-liquiflable'gas; and

such a gas is very desirable because it can safely be held and v confined within a thin-walledv containenSuch a gas is also desirable because a large amount of it can be held and confined within a small space, and because the pressure of that cuff.'T he-=presen t invention provides a control system for'a sphygmomanometer which'infla'tes'thje inflatable cuff of that sphygmoma'nometer ata relatively low rate during actual sensing of the blood pressure, but which inflates that inflatable cuff at a rapid rate during the initial pressurization of that in-' flatable cuff after'eachperiod wherein all pressure'was released from that inflatable cuff. lt-is, therefore, an objectof the present invention to provide a control system for a sphy'g- I relatively low rate during actual sensing of a blood pressure,

but which inflates that inflatable cuff at a rapid rate during the' initial pressurization of that inflatable cuff after each period when all pressure was released from that inflatable cuff.

- The sphygmomanometer provided bythe present invention pressurizes theinflatable cuff thereof until a Korotkoff sound is developed. and thus makes certain that sufficient pressure is developed within 'thati'nflatable cuff to enable that sphygmomanometer to sense a;person's diastolic blood pressure.

That sphygmomanometer' then depressurizes the inflatable cuff thereof as long as a Korotkoff sound is being developed. and fora very short length of time thereafter, and thus makes certain the'pressure in that inflatable cuff fallsbelow'-but momanometer which inflates the inflatable cuff thereof at a throw switch 26 therein. As shown particularly by FIGS. 1 and.

gas will remain substantially constant at any given temperature. In'addition, thecompressed: gas used in th'e'sphygmomanometer prcovided by the present invention is a nonoxidizing, noninflammable gas, and thus is particularly. desirable for use in operating rooms and in pressurized chambers-Iris, therefore, an object of the present invention to provide a sphygrnomanometer which uses a readily liqui'tiable. nonoxidating, noninflamrnable' gas' to pressurize the inflatable cuff thereof. v v Other and further objects'and advantages of the present in.-

ve ntion should become'apparent from anexamin'atio'n of the drawing and accompanying description.

In the drawing and accompanying description a preferred embodiment of 'the present invention is shown and described but it is to be understood that'the' drawing and accompanying of FIG. I, but-it shows' 'the lid of that sphygmomanorneter' in raised position, i

1G. 3 isa block diagram of the control system for the sphygmomanorneterof'FIGS.land 2, and FIG. 4 is a schematic diagram of that control system- COMPONENT-S- OF CONTROL SYSTEM Referring to the drawing inde'tail, the numeral 20 generally denotes a power supply which can have I17 volts, cycle, single phase, alternating current applied to the input thereof, which can develop 24 volts-DC at one output thereof, and which can develop 9 voltsDC at the other output thereof. A lead 22 and alead 24 can 'connectthe input of that'power supply to a suitable source of 117 volt, 60 cycle, single phase,

alternating current; and the lead 24 has a single pole, single j 2, that switch has a handle 25 which is readily accesible to the only a short distance below-the person's diastolic bloodpressure. It is, therefore, an objectof the present invention to PTO-5 vide a sphygmomanometer that pressurizes the inflatable cuff thereof until a Korotkotf sound is developed and'then depres-.

surize's that inflatable 'e'uff as, long as a Korotkoff sound is being developed and fora'very'shortlength of time thereafter. 1 Many sphygmomanonieters:utilize resilient'bulbs or air compressors to supply air'to the inflatable culfs'thereto to inflate those inflatable'cuffs'Z The useofa resilient bulb to operator of the sphygmomanometer. A conductor'27 is connected to that output of the power supply 20 which develops 24 volts DC, and a conductor is connected to the conduc tor. 27. A-conductorI31,- is connected to that outlet of the power supply 20 whichdevelops 9v volts The numeral 28 denotes .a microphone which candisposed adjacent an'ar'tery in the arm of a person;'and that. microphone preferably .is a shielded, dynamic microphone i which has an excellent low frequency response and allow irn-' --p.edance output. Such a microphone will provide an output v signal which will be relatively free from electrical noise picltup the inflatable cuff of 'a' -sphygmomanometer requires the from. Larry adjacent strong electromagnetic fields. That microphone will be set in register with the artery in the person's arm, and it will preferably be set so it is distal of an inflatable cuff 33 that will be wrapped around that arm. The numeral 30 denotes a capacitor which will couple the output of the microphone 28 to the base of an NPN transistor 38 and to the upper terminal of a capacitor 36; and the lower terminal of the latter capacitor is connected to ground. The capacitor 36 will bypass to ground any signals which are due to ambient noises, voices. and the like and which have frequencies materially above 40 cycles per second.

Resistors 32 and 34 are connected in series between conductor 31 and ground, and they constitute a voltage divider which will develop a positive voltage at the base of the transistor 38. A resistor 40 connects the collector of that transistor to the conductor 31, and parallel-connected resistor 42 and capacitor 44 connect the emitter of that transistor to ground. The transistor 38, resistors 32, 34, 40 and 42, and capacitor 44 constitutes a class A common-emitter temperature-stablized amplifier 39. The coupling capacitor 30 and the bypass capacitor 36 coact with the amplifier 39 to enable that amplifier to provide an excellent response to signals having frequencies close to 40 cycles per pound.

- The numeral 46 denotes a capacitor which is connected to the collector of transistor 38; and a junction 52 connects that capacitor to the base of a PNP transistor 56. A resistor 48 is connected between the junction 52 and conductor 31, and a junction 54 and an adjustable resistor 50 are connected between the junction 52 and ground. Parallel-connected resistor 58 and capacitor 60 are connected between the emitter of transistor 56 and conductor 31, and a resistor 62 is connected between the collector of that transistor and ground. The resistor 48 and the adjustable resistor 50 are conhected in series between conductor 31 and ground, and they constitute a voltage divider which will develop a positive voltage at the base of transistor 56. Transistor 56, resistors 48, 58 and 62, adjustable resistor 50, and capacitor 60 constitute a class A amplifier with an adjustable bias; and that amplifier is denoted by the numeral 57. j

A capacitor 64 is connected between the collector of transistor 56 and ground, and it constitutes a low pass filter. That capacitor will filter out random noise which is generated, or picked up, by the amplifiers 39 and 57.

The numeral 68 denotes an NPN transistor; and the emitter of that transistor is directly connected to ground. A resistor 70 connects the collector of that transistor to the conductor 31; and a Zener diode 66 connects the collector of transistor 56 to the base of transistor 68. That Zener diode establishes a threshold value which must be exceeded by any signals at the collector of transistor 56 before the transistor 68 can be rendered conductive. The no signal voltage at the cathode of that Zener diode can be adjusted by appropriate adjustment of the movable contact of the adjustable resistor 50.

A capacitor 72 is connected between the lower terminal of resistor 70 and ground, and it will coact with that resistor to constitute a rate circuit. 1n the said one preferred embodiment of sphygmomanometer, the time constant of that rate circuit is exactly three seconds. The transistor 68, Zener diode 66, resistor 70 and capacitor 72 constitute a level discriminator and signal detector, and that level discriminator and signal detector is denoted by the numeral 69.

The numeral 74 denotes an NPN transistor; and the emitter of that transistor is connected to ground by a Zener diode 78, while the collector of that transistor is connected to the conductor 31 by a resistor 76. A diode 80 has the anode thereof connected to the collector of that transistor, and has the cathode thereof connected to the base of an NPN transistor 82 by a junction 81. The transistor 74, resistor 76, Zener diode 78, and diode 80 constitute a level-controlled electronic switch; and that level-controlled electron switch is denoted by the numeral 83. That level-controlled electronic switch will be actuated whenever the voltage across the capacitor 72 reaches a predetermined level-and that voltage will reach that level 1 42/100 of a second after that capacitor starts to charge after it positive feedback for the transistor 56 and thereby assure full discharging of the capacitor 72.

' The emitter of the transistor 82 is connected to ground by a I Zener diode 86. while the collector of that transistor is con nected to conductor 27 by'the coil 84 of a relay 85. That relay has a movable contactand fixed contacts 92 whenever the relay coil 84 is deenergized, but will engage the fixed contact 94 whenever that relay coil is energized. A resistor 88 is connected in parallel with the series-connected relay coil 84 and the collector-emitter circuit of transistor 82. That resistor and Zener diode 86 will establish a regulated voltage at the emitter of that transistor. The transistor 82 and the Zener diode 86 constitute a driver for the relay 85; and that driver is generally denoted by the numeral 87.

A lamp 96 is connected between the fixed contact 94 and ground, and that lamp preferably is an amber lamp. A lamp 98 is connected between the fixed contact 92 and ground, and that lamp preferably is a green lamp. A solenoid 100 of 21 normal pressurization valve 10lalso is connected in parallel with the lamp 98. A discharge diode 102 is connected in parallel with the solenoid 100. The valve 101 will be closed whenever the solenoid 100 is deenergized, but it will be open whenever that solenoid is energized.

The numeral 104 denotes'an NPN transistor which has the collector thereof connected to the conductor 29; and the emitter of that transistor is connected to ground by the coil 106 of a relay 111. That relay includes movable contacts 108 and 110 and fixed contacts 112, 114 and 116. The movable contact 108 will engage the fixed contact 112 and the movable contact 110 will engage the fixed contact 116 whenever the coil 106 is deenergized; but the movable contact 110 will move out of engagement with the fixed contact 116, and the movable contact 108 will move out of engagement with the fixed contact 112 and into engagement with the fixed contact 114 whenever the coil 106 is energized. A resistor 118 is connected between the fixed contact 112 and the conductor 29, and an adjustable resistor 120 is connected between the fixed contact 114 and ground. A solenoid 122 of a fast pressurization valve 123 is connected between the movable contact 110 and ground. That valve will be closed whenever the solenoid 122 is deenergized, but it will be open whenever that solenoid is energized. A discharge diode 124 is connected in parallel with the solenoid 122.

A junction 126 and a capacitor 128 connect the base of the transistor 104 to ground. A junction 130 and a capacitor 132 connect the movable contact 108 will move out of engagement with the fixed contact 112 and into engagement with the fixed contact 112 and into engagement with the fixed contact 114 whenever the coil 106 is energized. A resistor 118 is connected between the fixed contact 112 and the conductor 29, and an adjustable resistor 120 is connected between the fixed contact 114 and ground. A solenoid 122 of a fast pressurization valve 123 is connected between the movable contact 110 and ground. That valve will be closed whenever the solenoid 122 is deenergized, but it will be open whenever that solenoid is energized. A discharge diode 124 is connected in parallel with the solenoid 122.

A junction 126 and a capacitor 128 connect the base of the transistor 104 to ground. A junction 130 and a capacitor 132 connect the movable contact 108 of the relay 111 to ground. A resistor 134 connects the junction 130 to the base of an NPN transistor 136; and the collector of that transistor is connected to the conductor 29, while the emitter of that transistor is connected to ground by a resistor 138. The transistor 136 is connected as an emitter follower; and the emitter of that transistor is connected to the base of an NPN transistor 142 by a resistor 140. The emitter of the latter transistor is connected directly to ground, but'the collector of that transistor is connected to the conductor 29 by the coil 144 ofa relay 159. That I contact 150 and ground; and an adjustab relay has movable contacts 146 and 148 and has fixed contacts 150, 152 and 154. The movable contact 146 will be in engagement with the fixed contact 150 and the movable contact 148 will be in engagement with the fixed contact 154 whenever the relay coil 144 is deenergized; but the movable contact 148 will move out of engagement with the fixed contact 154, and the movable contact 146 will move out of engagement with the fixed contact 150 and into engagement withdthe fixed contact 152 whenever that relay coil is energize l A solenoid 156 of a fast depressurization valve 157 is connected between the movable contact l48and ground. That valve will be closed whenever the solenoid 156 is deenergized,

but it will be open whenever that sol noid is energized. A discharge diode 158 is connected in parallel with the solenoid 156. A resistor 160 and the movable and fixed contacts 148 and 154 of the relay 159 normally connect the junction 81 adjacent the base of transistor 82 to the conductor 29.

An adjustable resistor 162 is conneclted between the fixed le resistor 164 is connected between thefixed contact 152 and the conductor 29. The capacitors 128 and 132'and the adjustable resistors 120 and 164 constitute a fastpressurization and depressurization timing circuit; and that circuit is generallydenoted by the numeral 166. Y Y

The numeral 170 denotes a container of a readily liquifiable gas; and, while different gases could be used, Freon 114 has been found to be a very desirable liquifiable gas. That gas will develop a pressure of 36 pounds per square inch at a temperature of 25 entigrade, and it is nonoxidizing and vnonin flammable. That container can be quite small-being approximately 3% inches in diameterand 7 inches high. The numeral 172 denotes a similar container of a readily liquifiable gas. As indicated particularly by FIG. 3, the outlet of the container 170 is connectable to a reservoir 178 bythe fast pressurization valve 123 and an adjustable-fast pressurization orifice 174. Also, as indicated particularly by FIG. 3, the outlet of the container 172 is connected to the reservoir 178 by the normal pressurization valve 101 and an adjustable normal pressurization orifice 176. Thatreservoir is continuously connected to is connected to that conduit. Normally the valve 186 is closed,

but it can be opened to vent gas to the atmosphere by the mere application of finger pressure to that valve. A manometer 190 is connected to the inflatable cuff 33, and the level of the mercury within that manometer will indicate theblood pressure of I .the person.

The inflatable cuff 33, the manometer 190, and the housing 192 therefor. are standard and usual components of a sphygmomanometer. That housing rests upon and is secured to an enclosure 194; and that enclosure supports and encloses the reservoir 178, the orifices 174, 176 and 180, the valves 101, 123, 157, 182 and 186, andmost of the electrical components of the control system. Asshown by' FIG. 1, the handle 25 of the switch 26 and the lamps 96 and 98 project upwardly through the enclosure "1 94- -to make that handle readily accessible to, and to make those lamps readily visible to, the operator of that control system. The containers 170 and 172 are releasably secured to. the enclosure 194 by clamps 196; and they are releasably connected to the valves 123 and 101, respectively, by readilyseperable pressure tight connections of standard design. I

6 OPERATION OF CONTROL SYSTEM ln using the said preferred embodiment of control system provided by the present invention, the microphone 28 can be taped to a persons arm in register with an artery within that arm; and the inflatable cuff 33 can be secured to that persons arm. Preferably, the microphone 28 will be located distally of that inflatable cuff. The leads 22 and 24 can then be connected to the source of one hundred and seventeen volts, sixty cycle, single phase alternating current, and the switch 26 can then be closed. Thereupon, current will flow from conductor 27 via the resistor 88 and the Zener diode 86 to ground; and that current flow will establish a regulated positive DC voltage at the emitter of the transistor 82-thereby establishing a threshold at the base of that transistor. Conductor 29, the fixed and movable contacts 154 and 148 of the relay 159, and the resistor 160 will apply approximately 24 volts to the junction 81; and that voltage will back-bias the diode 80, and will cause sufficient current to flow through the base-emitter circuit of transistor 82 and Zener diode 86 to render that transistor conductive. The resulting flow of current from conductor 27 via relay coil 84, transistor 82, and Zenerdiode 86 will energize that relay coil; and, as the movable contact 9110f relay moves out of engagement with fixed contact 92 and into engagement with fixed contact 94, the lamp 98 will darken, the solenoid 100 of the normal pressurization valve 101 will become deenergized and that valve will close, and the lamp 96 will become illuminated. Current also will flow from conductor 29 via resistor 118 and the fixed and movable contacts 112 and 108 of relay 111, junction 130, and capacitor 132 to ground. in less than a second, the voltage across that capacitor will be large enough to force current to flow from junction via resistor .134, the base-emitter circuit of transistor 136, and resistor 138 to ground; and that flow of current will render that transistor conductive. The resulting positive voltage at the base of transistor 142 will render that transistor conductive; and hence current will then flow from conductor 29 via relay coil'l44 and transistor 142 to ground. The resulting energization of that relay coil will shift the movable contact 146 out of engagement with the fixed contact 150 and into engagement with the fixed contact 152, and also will shift the movable contact 148 out of engagement with the fixed contact 154. Shifting of movable contact 148 out of engagement with the fixed contact 154 will deenergize the solenoid 156 of the fast depressurization valve 157, and will thereby permit that valve to close; and also will disconnect resistor 160 and junction 81 from the conductor 29, and will thus remove the large voltage at the junction 81. The reverse bias on the diode 80 will thus be removed; and, thereupon, current will flow from conductor 31 via resistor 76, diode 80, junction 81, the base-emitter circuit of transistor 82, and Zener diode 86 to ground to keep that transistor conductive. Current also will flow fromconductor 29 via the fixed and' movable contacts 116 and 110 of relay 111 and the solenoid 122 of the fast pressurization valve 123 to ground; and the resulting energi'zationof that solenoid will open that valve. Thereupon, gas from the container will flow through the fast pressurization valve 123, the orifice 174, the reservoir 178, and the conduit 184 to the inflatable cuff 33. As soon as ground; and that flow of current will slowly charge that capacitor.

At the instant the switch 26 was closed, current also flowed from conductor 31 via resistors 32 and 34 to ground; and the resulting positive voltage at the base of transistor 38 rendered that transistor conductive. Current also flowed from conductor 31 via'resistor 48 and adjustable resistor 50; and the resultt ing voltage drop across the resistor 48 made the base of transistor 56 sufficiently less positive than the emitter of that transistor torender thattransistor'conductive. The voltage drop across the resistor 62 will establish a positive voltage at the cathode of Zener diode 66', but that voltage will be less than the breakdown voltage of that Zener diode, and hence that Zener diode and the transistor 68 will remain nonconductive. Current also flowed from conductor 31 via resistor 70 and capacitor 72 to ground; and that current flow quickly charged that capacitorthe voltage at the upper terminal of that capacitor, and hence at the base of transistor 74, rising in 1 42/100 of a second to a value which exceeded to the threshold at the base of that transistor and thus caused sufficient current to flow through the base-emitter circuit of that transistor to render that transistor conductive. The resulting low voltage at the anode of the diode 80 back-biased that diode; and, thereupon, the transistor 82 became nonconductive. The resulting deenergization of relay coil 84 permitted the movable contact 90 to move out of engagement with fixed contact 94 and into engagement with fixed contact 92; and, thereupon, the lamp 96 darkened, the lamp 98 became illuminated, and the solenoid 100 of the normal pressurization valve 101 became energized and opened that valve. At that time, compressed gas flowed from container 170 via fast pressurization valve 123, orifice 174, and reservoir 178 into the inflatable cuff 33', and compressed gas also flowed from container 172 via normal pressurization valve 101, orifice 176 and reservoir 178 to that inflatable cuff. The conjoint flow of compressed gas from both of the containers 170 and 172 quickly increased the level of the pressure within the inflatable cuff 33.

All of this means that as the switch 26 was closed, the fast depressurization valve 157 was permitted to close, the fast pressurization valve 123 was opened, and the normal pressurization valve 101 was permitted to close for slightly less than 1% seconds and then was caused to open. As a result, compressed gas rapidly flowed into the inflatable cuff 33, and the pressure within that inflatable cuff started to rise. The lamp 98 was illuminated to indicate that the pressure within that inflatable cuff was rising.

It would be desirable to permit the fast pressurization valve 123 to close after the pressure in the inflatable cuff 33 rose to 40 millimeters of mercury; and hence the movable contact of the adjustable resistor 164 is set to charge the capacitor 128 at a rate which will make the voltage at the junction 126 sufficiently positive to render the transistor 104 conductive by the time the pressure in that inflatable cuff has risen to 40 millimeters of mercury. ln the said one embodiment of control system, the capacitor 128 will charge for a period of about three seconds before the transistor 104 becomes conductive; and as that transistor becomes conductive the relay coil 106 will become energized, and the movable contact 108 will move down out of engagement with fixed contact 112 and into engagement with fixed contact 114, and the movable contact 110 will move down out of engagement with fixed contact 116. The shifting of the movable contact 110 out of engagement with the fixed contact 116 will deenergize the solenoid 122 of the fast pressurization valve 123, and will thereby permit that valve to close. The shifting of the movable contact 108 out of engagement with fixed contact 112 will halt the charging of capacitor 132; and the shifting of that movable contact into engagement with fixed contact 114 and will enable that capacitor to start discharging via junction 130, movable and fixed contacts 108 and 114, and adjustable resistor 120 as well as via junction 130, resistor 134, the base-emitter circuit of transistor 136, and resistor 138. That capacitor will discharge for a predetermined period of time, which will be determined by the setting of the movable contact of the adjustable resistor 120; and, in the said embodiment of control system, that predetermined period of time is about 4 minutes. The current flowing from the upper terminal of that capacitor via junction 130, resistor 134, the base-emitter circuit of transistor 136, and resistor 138 will keep that transistor conductive throughout that predetermined period of time; and will thus keep the fast depressurization valve 157 closed throughout that predetermined period of time.

Compressed gas will continue to flow from container 172 through the normal pressurization valve 101 and the orifice 176 into the reservoir 178, and thence into the inflatable cuff 33. Consequently. the pressure within that cuff. and in the manometer 190, will continue to increase-although at a lesser rate. As the pressure within that inflatable cuff increases, that pressure will attain a value which'will enable that tor 36 will coact with the resistor 34 and with the input impedance of the transistor 38 to attenuate signals appreciably above forty cycles per second. The transistor 38 will amplify the signals corresponding to the first of the Korotkoff sounds; and the resulting amplified and inverted signals will appear at the collector of transistor 38. Those amplified and inverted signals will be coupled to the base of transistor 56 by capacitor 46 and junction 52', and they will render that transistor more conductive. The resulting increased voltage across the resistor 62 will enable the voltage at the cathode of the Zener diode 66 to exceed the breakdown voltage of that Zener diode, and, thereupon, current will flow from conductor 31 via resistor 58, the emitter-collector circuit of transistor 56, Zener diode 66, and the base-emitter circuit of transistor 68 to ground. That flow of current will render the latter transistor conductive; and the voltage at the collector of that latter transistor will tend to fall to ground potential. The capacitors 72 and 89 will discharge through the transistor 68, and the ensuing voltage drop across the latter capacitor will make the base of transistor 56 even more negative. The latter transistor will become even more conductive, and will further increase the positive voltage at the base of transistor 68. The resulting regenerative action between the transistors 68 and 56 will drive the former transistor into saturation; and that transistor will promptly-in less than one-tenth of a second-discharge the capacitor 72. While that capacitor is discharging, it will tend to make the left-hand terminal of capacitor 89 more negative than the right-hand terminal of that capacitor, and thus will tend to keep the transistor 56 more conductive. While the capacitor 72 is still discharging, the voltage at the base of transistor 74 will fall sufficiently toward ground potential to drop below the threshold which the Zener diode 78 establishes at that base; and, thereupon, that transistor will become nonconductive. As that transistor becomes nonconductive, a positive-going voltage will develop at the collector thereof, and thus at the anode of diode and that voltage will forward-bias that diode and thus permit current to flow from conductor 31 via resistor 76, diode 80, junction 81, the base-emitter circuit of transistor 82, and Zener diode 86 to ground; and, thereupon, the latter transistor will become conductive. The consequent flow of current from conductor 27 via relay coil 84, transistor 82 and Zener diode 86 will again energize that relay coil and will again cause the movable contact to move out of engagement with the fixed contact 92 and into engagement with the fixed contact 94. As that movable contact moves out of engagement with the fixed contact 92, it will darken the lamp 98 and it also will deenergize the solenoid of the normal pressurization valve 101. lmmediately, that valve will close; and no further compressed gas will be introduced into the inflatable cuff 33. Gas will continue to vent from that inflatable cuff through the normal depressurization orifice 180; and hence the pressure in that inflatable cuff, and in the manometer 190, will slowly decrease. The lamp 96 will be illuminated as the movable contact 90 moves into engagement with the fixed contact 94; and that lamp will indicate to the operator of the sphygmomanometer that the pressure in the inflatable cuff 33 is decreasing.

. depressurization of the inflatable cuff.

All of this means that the'compreSsed gas from the container 17-2 increasedthe pressure within the inflatable cuff 33 from 40 millimeters of mercury to whatever pressure was needed to enable that inflatable cuff to occlude the artery in the personsarm. As that artery was occluded, a contraction of the persons heart causeda series of Korotkoff sounds to develop; and the first of those Korotkoff sounds caused the transistor 82 to' become conductive, and thereby terminated the pressurization of the inflatable cuffg33 and initiated the -As the capacitor 72- becomes substantially completely. discharged, the voltage at the right-hand'terminal of the .capacitor 89 will no longer be more positive than the voltage at the left-hand terminal of thatcapacitor; and, consequently, the conductivity of the.transi stor 56 wiill fall to its normal level. The resulting decrease-in voltag dro'p'across the resistor 6 2 will permit the transistor 68 to become nonconductiveonce again; and at such'time the c pacitor 72 will again start charging. However.' .the.secondof he Korotkoff sounds caused by thezcontraction of thepers ns heart will again render the transistor 68 -conductive, and thus again discharge vthe c'apacitor 72. As that capacitor dis harges, it will again coact with the capacitorflilto make t e transistor 56 more conductive; and the ensuing regenerative action betweenthe transistors 56 and 68 will'again'drive'the'latter transistor into saturation, and will again 'dischargethe capacitor 72. Thereupon, the transistor 68 will again become nonconductive, and the capacitor 'lzwill again start .to charge. The succeeding Korotkoff sounds caused by the said contraction of the persons heart will cause-further discharging of the capacitor 72', and will'thus keep the voltage. across that capacitor from increasing s'ufficiently'to exceed the threshold which the'Zener diode establishes at the base of transistor 74". As a result that transistor will remain nonconductive. The overall result is that as long as the r'nicrop'honej28 senses any of the Korotkoff sounds caused by the saidv contraction of the persons heart,

the transistor74 will remain nonconductive and thetransistor 82.will keep the'relay coil 84 energized -and the pressure in the inflatable cuff 33 will continue to fall at a slow rate.

' -lf the microphone 28 failsto sense any Korotkoff sounds for l 42/ 10.0 of a second; the resulting uninterrupted charging of thecapacitor 72'will make-the voltage across that capacitor great enough to exceedfthe threshold which the Zene'r diode 7,8. establishes at the. baseof transistor 74; and, thereupon, that transistorwill become conductive. 'As that transistor becomes conductive, it-will back-bias the diode 80 and thus keep further-current from flowing'from conductor 31 via resistor 76, diode 80, junction 81', the base-emitter circuit of transistor 82, and Zener diode ,Itoiground. Thereupon, the latter transistor will become nonconductive, the relay coil sewn! become deenergized,and the lamp 96'will become dark while I the lamp 9? will become illuminated and the solenoid 100 will become reenergized. f

This means that thede'pressurizationof inflatable cuff 33 began'as the first Ko'rotkoffsound, of a series of Korotkoff sounds, was heard,.that suc h depressuri'zation was continued throughout theiduration of thatseries of Korotkoff sounds,

and that such'depressurization was concluded 142/100 of a *second after the last Korotkofi' sounds, of that series of Korotkoff sounds, was sensed by rnicrophone'28. In continuing the 1 depressurimtion .of inflatable cuff '33 for just less than I flatable cuff again occludes the artery in the persons arm, and

causesa second group-of Kortkoff sounds to develop. As the first- Korotkoff. sound of that second group of Korotkoff sounds is sensed by the microphone 28, the transistor 56 will againbe rendered more conductive, and will again render the transistor 68 conductive. Theensuing discharging of capacitor I 72' will'again render the transistor 74 nonconductive; and a further depres'surization of the inflatable cufl" 33 will be initiated. That depressurization will continueas longas any Korokoff sound of that second'group of Korotkoff sounds is sensed by the microphone 28; and that depressurization'will continue for l 42/100,0f a second thereafter. When that microphone fails, for a period of '1 42/100 of a second, to

sense a Korotkoff sound, the transistor '74 will again become conductive-and the second depressuri'zation of the inflatable cuff 33willend and a further repressurization of that inflata ble cuff will begin. I I

It should thus be clear that the control system for sphygmomanometer provided 'by the present invention will recurrently raise the pressure in the inflatable cuff 33 to a value slightly above the persons diastolic blood pressure and will then permit that pressureto fall to a value slightly below that person's diastolic blood-pressure. The total change in pressure within that inflatable cuff, and hence in the manometer 190.. will be the equivalent of just a few millimeters of mercury and, consequently, that manometer will provide a substantially'steady pressure level indication-Such a pressure level indication will enable the operator of the sphygmomanometer to I readily determine the persons'diastolic blood pressure.

1 The discharging of the capacitorl32, which began when the coil 106 of relay 111 became energized and moved the movable contact 108 down into engagement with the fixed contact 114, will continue throughout. the recurring pressurizations and depressurizations of'the inflatable cuff 33. Specifically,

current will flow fromj'the upper terminal of capacitor 132 via junction 130, resistor' 134,' thebase-emitter circuit of transistor 136,'and resistor 138 to the lower terminal of that capacitor, and also frorn'the upperterminal of that capacitor via junction 130, movable and fixed contacts 108 and. 114,

and adjustable resistor 120 to the lower terminal of that capacitor. After about; 4 minutes, the voltage across the capacitor 132'will decrease to the point where the current flowing through the base-emitter circuit of transistor l36will be too small to keep that transistor conductive; and, thereupon, that transistor will become nonconductive. The resulting negative-going voltage at the emitter thereof will render the transistor .142 nonconductive-, 'and will thus deenergize the 144 of relay 159. The' movable contact 146 of that relay will then move up out of engagementwith fixed contact 152 and into engagement with fixed contact 150, and the movable con- Wseconds after each Korotkoff sound is sensed by. the

microphone; the control systemof the sphygmomanometer provided by the present invention provides sufficient timeflfor a further. Korotkolf sound, of the series of Korotkoff sounds, to cause afurther discharging of the capacitor; and thus causes the depressurizjation of that. inflatable cuff. to continue throughout the duration of that series of Korotkoff sounds. In

tact 148 will move up into engagement with fixed contact 154, Thereupon, the fixed andmovable contacts l54and 148 of relay 159 and the resistor 160 will again connect conductor 29 to the junction 81; and the resulting application of about 24 volts to that junction will again back-bias the diode and will again render the transistor 82 conductive. The" ensuing energizationofrelay coil 84 will again illuminate lamp 96, darken lamp 98,.and-deenergizesolenoid of the, normal prescontinuing the depressur'ization of the inflatable cuff 33 throughout the duration of that series of Korotkoff soundsthat control system makescertain that the pressurein that inflatable'euff does fall below thelevel of the personsdiastolic blood pressure. and that repressurization of that inflatable cuff can surization valve 10l-with consequent cessation of the pres-' I 'sur'ization of the inflatable cuff-33. I 4

As the movable contact 1'48 of the relay 159 moved into engagernent with fixed contact-154', current began to flow from.

. conductor Z9 via fixed and movable contacts 154 and '148 and solenoid lS6 of, the 'rapid depre'ssurization valve 157 to ground; and the resulting opening of that valve quickly depressurized the inflatable cuff 33 and the reservoir 178. That depressurization is desirable, because it will substantially completely relieve the pressure on the person's arm; and that relief ofpressure is important in minimizing discomfort ofthat person and in protecting that persons arm from injury. Moreover, that relief of pressure is important, because it will keep the diastolic blood pressure of that person from shifting- -as it could do if the blood pressure of that person was being sensed continuously.

As the movable contact 146 of relay 159 moved back up into engagement with the fixed contact 150, the capacitor 128 tended to discharge via movable and fixed contacts 146 and 150 and adjustable resistor 162, and also via the base-emitter circuit of transistor 104 and relay coil 106. The resulting flow of current through that base-emitter circuit will keep that transistor conductive, and thus will enable that transistor to keep that relay coil energized. That relay coil will be kept energized for a predetermined length of time; and, in the said preferred embodiment of sphygmomanometer provided by the present invention, that relay coil will be kept energized for one minute. As a result, the normal and fast pressurization valves 101 and 123 will remain closed, and the fast depressurization valve 157 will remain open, for one minute. The pressure within the inflatable cuff 33 will fall to the ambient level, and substantially no pressure will be applied to the persons arm for that period of time.

At the end of that one minute, the voltage across the capacitor 128 will decrease sufficiently to permit the transistor 104 to become nonconductive; and, as that transistor becomes nonconductive, the relay coil 106 will become deenergized and the movable contacts 108 and 110 will move back up into their normal positions. Current will immediately flow from conductor 29 via resistor 118, fixed and movable contacts 112 and 108, junction 130 and capacitor 132 to ground; and, in less than one second, transistor 136 will become conductive and will render transistor 142 conductive-with a consequent energization of coil 144 of relay 159. Thereupon, movable contact 148 will again move downwardly, and movable contact 146 will again move out of engagement with the fixed contact 150 and into engagement with the fixed contact 152. Shifting of movable contact 148 out of engagement with the fixed contact 154 will deenergize the solenoid 156 of the fast depressurization valve 157, and will thereby permit that valve to close once again; and also will disconnect resistor 160 and junction 81 from the conductor 29, and will thus again remove the large voltage at the junction 81. Current also will flow from conductor 29 via the fixed and movable contacts 116 and 110 of relay 111 and the solenoid 122 of the fast pressurization valve 123 to ground; and the resulting energization of that solenoid will again open that valve. Thereupon, gas from the container 170 will again flow through the fast pressurization valve 123, the orifice 174, the reservoir 178, and the conduit 184 to the inflatable cuff 33. As soon as the movable contact 150 of relay 159 moves down into engagement with the fixed contact 152, current will again flow from conductor 29 via adjustable resistor 164, fixed and movable contacts 152 and 146, junction 126, and capacitor 128 to ground; and that flow of current will slowly charge that capacitor. Because the pressure within the inflatable cuff 33 will be too low to enable that inflatable cuff to occlude the person s artery, no Korotkoff sounds will be present; and hence the capacitor 72 will be charged and the transistor 74 will be conductive. The diode 80 will be back-biased and hence the transistor 82 will be nonconductive; and, as a result, the relay 85 will illuminate the lamp 98 and will energize the solenoid 100 of the normal pressurization valve 101.

The overall result is that at the end of the four minute pressure relief period, the fast depressurization valve 157 will again reclose, the fast pressurization and the normal pressurization valves 123 and 101 will again reopen, and the inflatable cuff 33 will again be pressurized at a rapid rate. After about three seconds, the transistor 104 will again become conductive, and will again energize the coil 106 of relay 111. The ensuing shifting of movable contacts 108 and 110 downwardly will again deenergize the solenoid 122 of the fast pressurization valve 123, and will again limit further pressurization of the inflatable cuff 33 to the normal pressurization rate. The shifting of the movable contact 108 down into engagement with the fixed contact 114 will again start the four minute discharging period ofthe capacitor 132.

Thereafter, throughout that one minute period. the sphygmomanometer provided by the present invention will successively increase and pressure within the inflatable cuff 33 to cause Korotkoff sounds to develop, will decrease that pressure until those Korotkoff sounds disappear, and will then continue to decrease that pressure for 142/100 of a second thereafter. The pressure in that inflatable cuff, and hence in the manometer 190, will hover closely around the persons diastolic blood pressure; and that blood pressure can be easily read by the operator of the sphygmomanometer. Each four minute pressure-sensing period will be succeeded by a one minute pressure relief period; and hence generally continuous sensing of the person's diastolic blood pressure can be provided without undue discomfort for that person.

In the event a person's diastolic blood pressure is less than forty millimeters of mercury, Korotkoff sounds can render the transistor 68 conductive, and can thus cause the relay to deenergize the solenoid of the normal pressurization valve 101 prior to the time the capacitor 128 is charged sufficiently to render the transistor 104 conductive. This means that the fast pressurization cycle will be initiated while both the fast pressurization and normal pressurization valves 123 and 101 are open but will be terminated while only that fast pressurization valve is supplying compressed gas to the inflatable cuff 33. Further, it means that as soon as the fast pressurization valve 123 is closed, as the transistor 104 becomes conductive and deenergizes the relay coil 106, the depressurization of that inflatable c'uff will start. Thereafter, the pressure in that inflatable cuff will fall until no further Korotkoff sounds are heard, and will continue to fall for 1 42/100 of a second thereafter; and then the normal pressurization solenoid 100 will again be energized.

CONCLUSION The discharge diode 102 will constitute a low impedance path for the energy within the solenoid 100, and thus will quickly dissipate that energy whenever the coil 84 of relay 85 is energized. Similarly, the discharge diodes 124 and 158 will constitute low impedance paths, respectively, for the energy within the solenoids 122 and 156, and thus will quickly dissipate that energy whenever the coils 106 and 144 of relays 111 and 159 are energized.

The containers and 172 are small in size, but they are able to hold and confine very large amounts of gas; because that gas is readily liquifiable at room temperatures. Thus, each of those containers is able to hold and confine sufficient gas to pressurize the inflatable cuff 33 for 24 hours of blood pressure monitoring. If desired, a single, larger container of compressed gas could be substituted for the containers 170 and 172.

During the operation of the sphygmomanometer provided by the present invention, ambient noises may be able to cause the microphone 28 to supply signals to the base of transistor 68 which will render that transistor conductive. That transistor and the transistor 56 will provide the regenerative action which will cause prompt discharging of the capacitor 72; and the transistor 74 will become nonconductive and will render the transistor 82 conductivewith a consequent energization of the relay coil 84 and a consequent deenergization of the solenoid 100 of the fast pressurization valve 101. However, if no further signals are received from the microphone 28 which could again render the transistor 68 conductive, the capacitor 72 will recharge and will again render the transistor 74 conductive-with a'consequent rendering of transistor 82 nonconductive. a consequent deenergization of relay coil 84. and a consequent reenergization of solenoid 100. This means that while a noise which could cause the microphone 28 to render the transistor 68 conductive would deenergize the solenoid 100 of the fast pressurization valve 101, that deenergization of that solenoid would be short-lived and that solenoid would quickly become energized again and would again open the fast pressurization valve 101. Only where the transistor 68 is repeatedly rendered conductive over a short period of time, as when a group of Korotkoff sounds is developed, will the solenoid 100 of the fast pressurization valve 101 be kept deenergized beyond 1 42/100 of a second during the 4 minute pressure-sensing period of the sphygmomanometer.

The pressure-sensing period can be made longer or shorter than four minutes by adjusting the position of the movable contact of adjustable resistor 120. That period can be made as short as 30 seconds or as long as minutes. The fast pressurization period can be made longer or shorter than three seconds by adjusting the position of the movable contact of adjustable resistor 164. However, where that period is lengthened it will usually be desirable to make the orifice 174 smaller; and where that period is shortened it will usually be desirable to make that orifice longer. The pressure relief period can be made longer or shorter than one minute by adjusting the position of the movable contact of adjustable resistor 162. That period can be made as short as 10 seconds or as long as 10 minutes. By changing the size of the orifice 180, it is possible to change the normal pressurization rate and the normal depressurization rate. Preferably that orifice will be dimensioned to provide a normal pressurization rate of 2 millimeters of mercury per second and a normal depressurization rate of 2 millimeters of mercury per second. Such rates facilitate precise and accurate sensing of a persons diastolic blood pressure.

If it ever became desirable to manually release the pressure within the inflatable cuff 33, as when the switch 26 was opened while the inflatable cuff 33 was pressurized, the operator of the sphygmomanometer need only actuate the manually-released valve 186. Thereupon, the compressed gas within that inflatable cuff and within the reservoir 178 would vent to the atmosphere.

If desired, a piezoelectric transducer, an infrasonic capacitive pickup or transducer, or some other form of pickup or transducer which could effectively sense Korotkoff sounds could be substituted for the microphone 28. However, that microphone has been found to be very useful.

In any control system that utilizes Korotkoff sounds in the monitoring of blood pressure, extraneously developed sounds in the audio frequency range can constitute a problem. Some control systems attempt to meet that problem by using elaborate and complex filters to remove or attenuate signals generated by unwanted sounds; but elaborate and complex filters are expensive, and even the most elaborate and complex filters can not reject all signals generated by unwanted sounds having frequencies close to the frequencies of signals generated by Korotkoff sounds. The control system provided by the present invention effectively meets that problem by using the capacitors 30 and 36 and the resistor 34 to attenuate the signals generated by most unwanted sounds, by keeping the effect which the rest of those signals have upon the level discriminator and signal detector 69 from materially affecting the monitoring of a person's blood pressure, and by providing a short recovery time for that level discriminator and signal detector specifically, the capacitors 30 and 36 and the resistor 34 will attenuate all signals which have frequencies appreciably above and appreciably below 40 cycles per second; and thus will permit only a very limited number of signals generated by unwanted sounds to reach the level discriminator and signal detector 69. Those signals will cause that level discriminator and signal detector to discharge the capacitor 72, and will thereby cause the level-controlled electronic switch 83 to render the transistor 82 and the relay 84 conductive-with a consequent deenergizaton of the solenoid 100 of the normal pressurization valve 101. However. such deenergization will merely delay the pressurization of the inflatable cuff 33 and will not provide an incorrect or aberrated level for the mecury in the manometer 190. and will not provide any other undesirable result. Furthermore, the level discriminator and signal detector 69 has a recovery time of less than one and six-tenths seconds; and hence the effect produced by a signal generated by an unwanted sound can go virtually unnoticed. insofar as any significant effect that it might have upon the monitoring of a person's diastolic blood pressure is concerned. Moreover, any signal which is applied to the level discriminator and signal detector 69 while the capacitor 72 is discharging will have no effect at all. The recovery time provided for that level discriminator and signal detector is longer than the time intervals between the heart beats of most persons-and thus is long enough to prevent repressurization of the inflatable cuff 33 between the termination of the Korotkoff sounds due to one heart beat and the initiation of further Korotkoff sounds due to the next-succeeding heart beatbut is short enough to keep the pressure in the inflatable cuff 33 from dropping unduly if a signal corresponding to an unwanted sound reaches that level discriminator and signal detector. The overall result is that the control system provided by the present invention minimizes the effect which unwanted sounds can have upon it. and yet does not require an elaborate or complex filter.

Whereas the drawing and accompanying description have shown and described a preferred embodiment of the present invention, it should be apparent to those skilled in the art that various changes may be made in the form of the invention without affecting the scope thereof.

lclaim:

1. In a control system for sensing a blood pressure which has a transducer to develop signals in response to the interaction of arterial pressure and cuff pressure, an inflatable cuff that can be applied to the body of a person, a source of gas for said inflatable cuff, a valve connected to said source of gas and to said inflatable cuff to selectively permit gas to pass to said inflatable cuff, and pressure relief means connected to said inflatable cuff to vent gas and thereby permit the pressure on the gas in said inflatable cuff to decrease, the improvement which comprises means coupled from said transducer and tending to hold said valve in cuff-pressurizing position until said transducer senses said signals, and thereby make certain that the pressure in said inflatable cufi' will rise to a value at least as great as the diastolic blood pressure of said person, said means thereafter responding to the sensing of said signals by said transducer to cause said valve to shift to cutf-depressurifzing position and said means includes a timer resettable each time the transducer senses successive ones of said signals in each blood pressure measurement cycle to maintain said valve in said cuff-depressurizing position, and said means subsequently continuing to maintain said valve in cuff-depressurizing position for a short predetermined length of time after said transducer senses the last of said successive ones of said signals thereby making certain that the pressure in said inflatable? cuff will fall below the diastolic blood pressure of said person.

2. In a control system for sensing a blood pressure according to claim .1 whereby, said predetermined length of time is longer than the time interval between one of said signals which is effectively sensed by said transducer and is due to a given heartbeat of said person and one of said signals which is effectively sensed by said transducer and is due to the next-succeeding heartbeat of said person.

3. In a control system for sensing a blood pressure according to claim 2 wherein said timer comprises a capacitor, a charging circuit therefor, and a discharging circuit therefor, said changing circuit for said capacitor having means therein tending to charge said capacitor at least over a period equal to said short predetermined length of time whenever said transducer is not effectively sensing said signals, said discharging circuit for said capacitor having means therein tending to discharge said capacitor whenever said transducer effectively senses one of said signals, said discharging circuit for said capacitor being regenerative to provide rapid. substantially complete discharging of said capacitor. 

